1. Field of the Invention
This invention relates to the field of switching voltage regulators, and particularly to failure detection circuits for such regulators.
2. Description of the Related Art
Switching voltage regulators are widely employed due to their efficiency and low cost. A typical switching regulator is made from a pair of output transistors connected in series between an unregulated input voltage and ground, with an inductor connected between the junction of the two transistors and an output terminal. A controller alternately drives one or the other of the transistors to conduct, so that current is alternately conducted from the input voltage to the inductor, and from the inductor to ground. The voltage at the output terminal is regulated by adjusting the duty cycle of the complementary signals driving the two transistors.
It is often desirable to quickly detect when a switching regulator failure has occurred. For example, to increase xe2x80x9cupxe2x80x9d time, computer servers typically employ two or more switching regulators in parallel to provide redundant power. All the regulator outputs are bussed together and their respective regulators share the current load. If one regulator fails by, for example, no longer delivering its rated current to the server, the remaining regulators must make up the lost current. This can place undue stress on the remaining regulators which can lead to their failure, and eventually to failure of the server.
A circuit and method for detecting switching voltage regulator failures is presented, which is particularly advantageous when the outputs of multiple regulators are bussed together to provide a redundant power source.
The failure detection scheme is useful with either synchronous switching regulatorsxe2x80x94with an output stage having series-connected output transistors which are alternately driven on and off with every clock cycle, or non-synchronous regulatorsxe2x80x94with an output stage having a diode in series with an output transistor which is switched on and off with every clock cycle. The scheme requires sensing a parameter which, when the regulator is operating normally, transitions above and below a predetermined threshold during each clock cycle as the output transistors are switched on and off. A decision circuit tracks the sensed parameter, and produces an output which toggles during each clock cycle as long as the sensed parameter transitions above and below the threshold. A counter is connected to count the number of clock cycles that occur, and to toggle its output when a predetermined count is reached. The counter also has a reset input, which receives the output of the decision circuit. When the reset input is toggled by the decision circuit, the counter is reset to an initial value.
When the regulator is operating normally, the sensed parameter transitions above and below the predetermined threshold once per clock cycle. This causes the decision circuit output to toggle the reset input once per clock cycle, so that the counter never reaches the predetermined count and its output never toggles. If, however, a failure occurs which causes the sensed parameter to fail to transition above and below the threshold during a clock cycle, the reset input is not toggled and the count value increments during that clock cycle. If the failure persists for the predetermined number of clock cycles, the counter output toggles to signal a failure.
The failure detection circuit and method are particularly useful for a single multi-phase switching regulator, or when a number of switching regulators are connected in parallel to provide a redundant power source. In the latter case, each of the regulators is equipped with a respective failure detection circuit, and each of their respective counter outputs is monitored. If one of the regulators fails, as indicated by its counter output, the failed regulator can be replaced or the powered circuit turned off before additional failures occur.
Further features and advantages of the invention will be apparent to those skilled in the art from the following detailed description, taken together with the accompanying drawings.